Refrigeration apparatus and method

ABSTRACT

An energy management system may include a refrigeration apparatus. Heat rejected from that apparatus may be used for heating elsewhere. There may be cooling loads which may be prone to frosting. A defrosting apparatus is provided. It is segregated from the coolant distribution array. Recaptured heat of the refrigeration apparatus may be used to defrost the cooling load heat exchangers, in an alternating or cycling mode, as may be. The apparatus may be electronically controlled. Ammonia may be used in a primary refrigeration vapour cycle system. The apparatus may also use a secondary cooling loop or system, linked to the primary system. The secondary system may be a distribution system. The secondary system may use CO 2  as a heat transport medium. The coolant system may be an high pressure system, whereas the defrost system is a low pressure system. Separate circuits are provided for coolant and defrost.

FIELD OF INVENTION

This application relates to refrigeration apparatus.

BACKGROUND OF THE INVENTION

In refrigeration systems in which the cooling load involves passingmoist air over a heat exchanger having a surface temperature below thedew point temperature of the air, accumulation of frost on the heatexchanger has been a long-standing problem.

Quite typically, defrosting involves ceasing the flow of chilled coolantto the heat exchanger, and passing a heated heat transport mediumthrough the heat exchanger instead. Other methods of defrosting mayinclude hot water defrost, electric defrost, and warm air defrost. Inknown systems, the heat transport medium, namely the fluid selected asthe coolant, is used for both purposes. In the cooling mode, the coolantis taken from the receiver on the low pressure side of the equipment. Inthe heating mode the same fluid, heated by whatever means, is passedthrough the cooling apparatus instead. Defrost systems of this generaltype are shown and described, for example, in U.S. Pat. No. 6,481,231 ofVogel et al., issued Nov. 19, 2002, and in U.S. Pat. No. 4,102,151 ofKramer et al.

SUMMARY OF INVENTION

The following summary may introduce the reader to the more detaileddiscussion to follow. The summary is not intended to, and does not,limit or define the claims. The disclosure may disclose, and the claimsmay claim, more than one invention or more than one inventive aspect orfeatures of any such invention.

In an aspect of the invention there is a refrigeration apparatus. Therefrigeration apparatus has a heat exchanger. The heat exchanger has afirst flow path for an air cooling load to be chilled; a second flowpath defining an evaporator for a refrigerant fluid; and a third flowpath through which to conduct a defrost fluid. The second and third flowpaths are segregated from each other whereby refrigerant fluid in thesecond flow path is isolated from defrost fluid in the third flow path.

In a feature of that aspect of the invention, the first flow path is anambient air pressure flow path, the second flow path is a lowtemperature flow path where the fluid evaporates, and the third flowpath is a higher temperature flow path where the fluid does not changephase. In a further feature, the refrigerant fluid includes a heattransfer transport medium carried in the second flow path at atemperature below 0 C. The refrigerant fluid is carried at a pressure ofgreater than 100 psig. In a still further feature, the defrost fluid iscarried in the third flow path at a temperature greater than 0 C. Thedefrost fluid is carried at a pressure of less than 100 psig. In anotherfeature, the refrigerant fluid includes CO₂. In still another feature,the defrost fluid includes a fluid other than CO₂. In a further feature,the defrost fluid is a liquid, the liquid is a brine that includesglycol.

In still another feature of that aspect, the refrigeration apparatusincludes a cooling machine. The cooling machine has a work input, acooling output, and a heat rejection output. The cooling machine has aworking fluid that is other than CO₂. In still another feature, thethird flow path is operatively connected with a heat rejection output ofthe refrigeration apparatus whereby, in operation, the heat rejectionoutput is connected to heat the defrost fluid to be conducted throughthe third flow path. In yet another feature, the refrigeration apparatushas a controller operable selectively to direct refrigerant fluid to theheat exchanger during a first time period, and to direct defrost fluidto the heat exchanger during a second time period, the second timeperiod is different from the first time period.

In another feature, the refrigeration fluid is at least predominantlyCO₂; the defrost fluid is a brine that is other than CO₂; and the thirdflow path includes a portion in which the defrost fluid is heated byrecaptured waste heat rejected from the refrigeration apparatus. Instill another feature, the heat exchanger is a first heat exchanger. Therefrigeration apparatus further includes at least a second heatexchanger; and a cooling machine operable to chill CO₂ and to rejectheat. The cooling machine has a working fluid. The working fluid is atleast predominantly ammonia. There is at least a first receiverreservoir in which one of (a) the working fluid, and (b) the CO₂ ismaintained in liquid phase. There is a thermal reservoir in which tostore recaptured waste heat rejected by the cooling machine. The controlapparatus is operable selectively to direct chilled CO₂ to any of theheat exchangers, the control apparatus also is operable selectively todirect heated defrost fluid to respective ones of the heat exchangers attimes other than when chilled CO₂ is directed thereto.

In still another feature, the apparatus includes a cooling machineoperable to chill CO₂ and to reject heat. The cooling machine has aworking fluid. The working fluid is at least predominantly ammonia. TheCO₂ is chilled by heat exchange with cold ammonia, and the defrost fluidis warmed by heat rejected from hot ammonia.

In another aspect of the invention there is a refrigeration apparatus.It has a cooling machine having a work input, a cooling output, and aheat rejection output. A first heat exchanger is mounted to extract heatfrom a first cooling load. The first cooling load has a frost point. Afirst transport apparatus is connected to carry a first heat transfertransport medium that has been chilled by the cooling output of thecooling machine to the first heat exchanger to cool the cooling load. Asecond transport apparatus connected to carry a second, heated, heattransfer transport medium to the first heat exchanger. The secondtransport apparatus is segregated from the first heat transfer transportmedium whereby the first and second heat transfer transport media aresegregated from each other. When the first heat transport medium isdirected to the heat exchanger, the heat exchanger is operable at atemperature below the frost point of the first cooling load. When thesecond heat transport medium is directed to the heat exchanger, the heatexchanger is operable at a temperature above the frost point of thefirst cooling load.

In a feature of that aspect of the invention, the second transportapparatus is connected to receive heat from the heat rejection output.In another feature, the apparatus further comprises a thermal storagemember connected to receive heat from the heat rejection output, and thesecond transport apparatus is connected to receive heat from the heatrejection apparatus that has been stored in the thermal storage member.In another feature, the first transport apparatus is a low temperaturefluid transport apparatus operable at a temperature less than 0 C (or,alternatively, at a pressure of greater than 100 psig), and the firstheat exchanger defines an evaporator for the first heat transfertransport medium. In a further feature, the first heat transfertransport medium is CO₂. In another feature, the second heat transfertransport medium is other than CO₂. In a further feature, the secondheat transfer transport medium is a brine that includes glycol. Inanother feature, the cooling machine has a working fluid other than CO₂.In a further feature of that other feature, the working fluid of thecooling machine is at least predominantly ammonia. In still anotherfeature, the cooling machine is housed in a first location, the firstheat exchanger is housed in a second location, and the first location isindependently ventilated to external ambient.

In still another feature, the refrigeration apparatus includes areceiver reservoir for the working fluid of the cooling machine. Inanother feature, the apparatus comprises a receiver reservoir for thesecond heat transfer transport medium. In still another feature, thefirst transport apparatus is a transport apparatus operable attemperatures of less than 0 C. In another feature, the second transportapparatus is a high temperature transport apparatus having an operatingenvelope at temperatures greater than 0 C. In yet another feature, theapparatus includes at least a second heat exchanger mounted to extractheat from a second cooling load, the second cooling load having a frostpoint. In still yet another feature, the apparatus includes anice-making refrigeration load.

In another aspect of the invention there is a method of defrosting aheat exchanger. The heat exchanger has a first flow path for a moist aircooling load to be chilled; a second flow path defining an evaporatorfor a refrigerant fluid; and a third flow path through which to conducta defrost fluid. The second and third flow paths are segregated fromeach other whereby refrigerant fluid in the second flow path is isolatedfrom defrost fluid in the third flow path, the method comprisingconducting refrigerant fluid to second flow path in a first time period,during which frost accumulates on the heat exchanger; and conductingheated defrost fluid through the second flow path during a second timeperiod whereby the previously accumulated frost diminishes.

In a feature of that aspect, the method includes ceasing flow of therefrigerant during flow of the defrost fluid. In a further feature, themethod includes using CO₂ as the refrigerant fluid. In another feature,the step of conducting heated defrost fluid occurs at a temperaturegreater than 0 C. In a further feature, the method includes using abrine as the defrost fluid, the brine including glycol. In anotherfeature, the method includes using a refrigerating apparatus to chillthe refrigeration fluid, rejecting heat from the refrigeration apparatuswhile chilling the refrigeration fluid; and using the rejected heat toheat the defrost fluid. In a further feature, the method includes savingheat rejected at a first time, and using that rejected heat to heat thedefrost fluid at a later time. In still another feature, the methodincludes employing ammonia as a working fluid in the refrigerationapparatus. In yet still another feature, the method includes using heatrejected from the refrigeration apparatus also to address at least oneadditional heating load other than heating the defrost fluid. In anotherfeature, the method includes using refrigerant chilled by therefrigerating apparatus to address at least one additional cooling loadother than chilling refrigerating fluid for chilling the air coolingload of the heat exchanger. In a further feature, there is a pluralityof heat exchangers having air cooling loads, and the method includescycling refrigerant fluid and defrost fluid to the plurality of heatexchangers selectively whereby each heat exchanger has a defrost cycle.In another feature, the method includes using a refrigeration apparatusto chill the refrigeration fluid, and the method includes using CO₂ asthe refrigeration fluid.

In another aspect, there is an energy management system. The energymanagement system includes a refrigeration apparatus. The refrigerationapparatus is operable to reject heat. A heating load apparatus isconnected to be heated by the heat rejected from the refrigerationapparatus. The heating load apparatus includes a defrost apparatus. Aload management control system is operable at a first time to cause iceto be made at the refrigeration load ice sheet apparatus and to causeheat to be directed from the refrigeration apparatus to the defrostapparatus. The load management control system is operable at a secondtime to cause the thermal storage apparatus to be charge as a cold sinkand to cause heat to be directed from the refrigeration apparatus to theheating load apparatus.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

These and other features and aspects of the invention may be explainedand understood with the aid of the accompanying illustrations, in which:

FIG. 1 shows a schematic representation of an example of a refrigerationapparatus embodying principles of the invention;

FIG. 2 shows a schematic representation of an alternate example of arefrigeration apparatus to that of FIG. 1, showing a cascade system; and

FIG. 3 shows a schematic of a heat exchanger of the refrigerationapparatus of FIG. 1

DETAILED DESCRIPTION

The description that follows, and the embodiments described therein, areprovided by way of illustration of an example, or examples, ofparticular embodiments incorporating one or more of the principles,aspects and features of the present invention. These examples areprovided for the purposes of explanation, and not of limitation, ofthose principles, aspects and features of the invention. In thedescription, like parts are marked throughout the specification and thedrawings with the same respective reference numerals.

The scope of the invention herein is defined by the claims. Though theclaims are supported by the description, they are not limited to anyparticular example or embodiment, and any claim may encompass processesor apparatuses other than the specific examples described below. Otherthan as indicated in the claims themselves, the claims are not limitedto apparatuses or processes having all of the features of any oneapparatus or process described below, or to features common to multipleor all of the apparatus described below. It is possible that anapparatus, feature, or process described below is not an embodiment ofany claimed invention.

The terminology used in this specification is thought to be consistentwith the customary and ordinary meanings of those terms as they would beunderstood by a person of ordinary skill in the art in North America.The Applicants expressly exclude all interpretations that areinconsistent with this specification, and, in particular, expresslyexclude any interpretation of the claims or the language used in thisspecification such as may be made in the USPTO, or in any other PatentOffice, other than those interpretations for which express support canbe demonstrated in this specification or in objective evidence ofrecord, demonstrating how the terms are used and understood by personsof ordinary skill in the art, or by way of expert evidence of a personor persons of experience in the art.

In the discussion herein, a refrigeration machine, or chiller, is onethat draws heat from a heat source at a lower temperature, and rejectsheat to a heat sink at a higher temperature. Machines of this nature aresometimes referred to as heat pumps. In general, such a machine may be agas cycle machine or a vapour cycle machine, and will have a work input,a cooling load output, and a rejected heat output. The work input maycorrespond to the mechanical work required to drive a compressor (orcompressors) and may be supplied by an electric or hydraulic motor, orby an internal combustion engine, or other suitable power source.

The embodiments of refrigeration apparatus described herein may bevapour cycle machines employing a gas phase compressor (or compressors),whether single stage, multiple stage or cascade system; a high pressureside condenser whence heat is rejected from the working fluid and inwhich the working fluid changes phase from gas to liquid; a pressurereduction device which may be a nozzle or valve; and an evaporativedevice such as an evaporator in which chilled working fluid may absorbheat from air as it is cooled and in which the working fluid may“flash”, i.e., change phase, from liquid to gas as it extracts heat fromthe heat source to be cooled. Of course, whether a device is a heatingor cooling device has an aspect of arbitrariness depending on point ofview: An evaporator may be a heating device for the working fluid, butis equally a cooling device to the cooling load; the condenser is acooling device for the working fluid, but a heating device for themedium to which that heat is rejected.

A distinction is made herein between a primary, or direct, system, inwhich the working fluid passed through the compressor is also the coldside heat transfer transport medium circulated through a coolingdistribution array; and an indirect system in which there is a separateor secondary distribution array, which may employ a heat transfertransport medium that is either the same as, or different from, theworking fluid of the primary system in the refrigeration machine. In anindirect system the working fluid uses as its heat source a heatexchanger of the secondary system that forms the heat rejection side ofthe distribution or secondary system.

Where the heat transfer transport fluid of the secondary system is aphase changing fluid, the heat source heat exchanger of the primarysystem may function as the condenser of the secondary system, with thedistribution array of heat exchangers of the secondary systems being theevaporators of the secondary fluid.

Whether the system is a primary, or direct, system, or an indirectsystem having a secondary loop for distribution, where there is a phasechanging fluid in either the primary or the secondary loop there may bea receiver, or reservoir, in which to collect a portion of the heattransport medium, be it primary or secondary. Typically, a receiver maybe located on the low pressure side, downstream of the condenser andupstream of the evaporator.

In this specification there is reference to heat transfer transportmedia. In general this term refers to substances that are heated orcooled at one location, and cooled or heated at a distant location,thereby transferring heat between the two locations. Most typically,such media are fluids. Many fluids have been used as coolants,refrigerants, or heating fluids. The fluids may be liquid in one portionof their use in operation, and in gas form in another portion of theiruse or operation. Some fluids are single phase (whether liquid or gas)or two-phase (typically liquid and gas). In the refrigeration industrythese fluids are often coolants, and many of these fluids may bereferred to as a “brine” or “brines”. A brine can be a single phaseliquid, and, typically, the term “brine” is used where that liquid has afreezing point other than (generally lower than) the freezing point ofwater. Although perhaps historically the term brine may have beenderived from a liquid such as water having a salt in solution therein,such as to alter its freezing point, the contemporary use of the word“brine” includes substances that do not necessarily include dissolvedsalts such as alcohol, carbon dioxide (CO₂), ammonia (NH₃). The term“volatile brine” is sometimes used to describe a CO₂ system in which theCO₂ does not undergo compression, but is circulated as a cooling mediumand undergoes a phase change. Brines may also include such things asglycol (more properly, ethylene glycol), or partial mixtures of glycoland water. A brine may also be a two phase fluid, in which the brinematerial is at its boiling point, or in which one component (or more) ofthe mixture is in a gas phase, and another is in a liquid phase.

There is also discussion in this specification of “working fluids”. Inthe context of a refrigeration system, the “working fluid” is usedherein as a fluid in a primary refrigeration circuit or system that iscompressed in one stage, has heat withdrawn from it in another stage, isde-pressurized in a third stage, and has heat added to it in a fourthstage. Over the last 120 years many fluids have been used as workingfluids, including air, Freon (CFC's), HFC's, ammonia, and carbondioxide. There may also be “working fluids” used in secondary circuitssuch as the heat rejection piping array, and in the cooling distributionarray.

Ammonia may be chosen as a working fluid in the refrigeration cyclecompressor for a number of reasons. It is readily available; it isrelatively inexpensive; it dissipates relatively quickly and easily inair, it does not tend to cause lasting environmental damage in terms ofeither ozone depletion or greenhouse gas emissions if it leaks, and doesnot tend to present a long lasting toxicity problem when disposal isdesired; and, in ice making technology, there is a well-establishedlevel of knowledge and expertise in the industry in using ammonia.Further, the working range of pressures and temperatures for ammonia maytend to be suitable for the present purposes. Ammonia may tend to permitthe use of relatively common oil lubricants, as opposed to highlyspecialized (and expensive) hygroscopic oils. Ammonia may tend to permitsmaller pipe sizes, better heat transfer and smaller heat exchangers.Leaks may tend to be relatively easy to detect. Ammonia tends to berelatively tolerant of moisture in the system.

In the embodiments described, the logic of the system may dictate thatthe fluid in a particular conduit must flow in a particular direction.This may be indicated in the illustrations by arrowheads. Although pumpsand check valves may be indicated in the illustrations, it may beunderstood that each embodiment is provided with such circulation pumpsand check valves as may be appropriate to cause fluid to flow in thecorrect direction, without cluttering the illustrations with unnecessarydetail. It is also understood that systems shown and described hereinhave suitable pressure relief and surge protection, as would beunderstood by persons of skill without such features being shown.

Referring to the general arrangement of FIG. 1, a refrigerationapparatus is shown generally as 20. In general, refrigeration apparatus20 includes a cooling machine 22 that has a work input such as providedat compressors 24, 26 (which may be in parallel, or may be staged inseries). Refrigeration apparatus 20 also includes one or more heatrejection outputs, such as condensers 28; a working-fluid pressure dropapparatus 30, such as a nozzle or turbine or motor or work-extractingpump; and a cooling load output 32, such as at an evaporator 34. Theremay be more than one evaporator 34. The cooling load output 32 can alsobe thought of equivalently as a heat input to the system. A receiver oraccumulator, or reservoir 36 may also be included. Reservoir 36 may belocated downstream of condenser 28, and upstream of evaporator 34. Allof items 24, 26, 28, 30, 32 and 34 define elements of a primary circuit,or loop, or system, of a refrigeration machine such as cooling machine22.

Refrigeration apparatus 20 may be located in a building facility, suchas may have a cooling or refrigeration load, or a variety of such loads,indicated generally as 40. The facility may be a factory, such as a foodprocessing factory, but may also be any other facility having arefrigeration load. That refrigeration load may include first, second,third, and perhaps more, individual heating load members or elements,each of those cooling loads being represented generically by a heatexchanger, such as heat exchangers 42, 44 and 46. Each of heatexchangers 42, 44, 46 may be an evaporator. Each of heat exchangers 42,44, 46 is connected to the rest of refrigeration apparatus 20 by a heattransfer medium transport apparatus 50, which may have the form ofpipes, or piping, or conduits, however termed, for carrying the heattransfer transport medium, namely the coolant fluid. It may be that eachof heat exchangers 42, 44, 46 has its own independent circuit, or flowpath of piping, in a parallel and independently controllable path, orone or more units may be arranged in series depending on cooling loadsand needs in the facility.

In the embodiment shown in FIG. 1, transport apparatus 50 includesdelivery piping 52 that carries a first heat transfer transport medium,in the form of a chilled coolant, from a heat rejection heat exchanger,such as heat exchanger 34, to the refrigeration or cooling load or loads40, and such others as may be, that define a cold sink (or heat source)at which heat from loads 40 is added to the coolant, thus raising itsenthalpy. Transport apparatus 50 may also include return piping 54 thatcarries higher enthalpy (i.e., heated) coolant back to heat exchange 34.As may be understood, the cooling circuit, or loop, that includes items42, 44, 46, 50, 52 and 54 is a secondary loop, or secondary system, andit is a coolant distribution system or circuit or array, all of whichmay be indicated generally as 58. The secondary loop may include a pump48, although a pump may not be necessary in all applications. Thesecondary loop 58 may include a receiver 56. Receiver 56 may define areservoir for condensed coolant, and may be located downstream of heatexchanger 34 (which, in the context of secondary loop 58 may act as acondenser), and upstream of such of heat exchangers 42, 44, 46 ofcooling load 40 as may be.

Similarly, refrigerating apparatus 20 may include a transport apparatus60, which may have the form of pipes, or piping, or conduits, howevertermed, for carrying a second heat transfer transport medium from theheat rejection output of cooling machine 22 to heat exchangers 42, 44,46. Transport apparatus 60 may include delivery tubing or pipes orconduits, however called, indicated as 62, and return tubing, or pipes,or conduits however called, indicated as 64. Transport apparatus 60 maybe termed a defrost fluid transport apparatus, or circuit, or loop andmay have pumps, such as pump 74, control valves, and check valves as maybe appropriate.

On the heat rejection side, there may be heating loads 66, 68. Whetherthere are heating loads 66, 68 or not, refrigeration apparatus 20 mayinclude a thermal storage reservoir 70, which may have the form of atank 72 in which heated material may be retained. As noted, there may bemore than one condenser 28. In the embodiment of FIG. 1, there may be afirst condenser 76. Alternatively there may be both a first condenser 76and a second condenser 78. First condenser 76 may be connected viapiping manifolds 71 and 73 to thermal storage reservoir 70, and eitherthrough manifolds 71 and 73 or through reservoir 70 to heating loadssuch as loads 66, 68, or such other heating loads as the facility mayhave, including the defrost load fed by transport apparatus 60. Secondcondenser 78 of apparatus 20 may be an evaporative condenser 78. In theevent that either condenser 76 cannot extract enough heat from theprimary working fluid, or in the event that there is too much heatstored in thermal storage reservoir 70, that heat can be rejected toambient at second condenser 78. That is, second condenser 78 acts in twomodes. In a first mode, it exchanges heat from the heat rejection sideworking fluid to external atmosphere through one side or coil, with thereturn line running in effectively a parallel path back to receiver 36as opposed to coolant passing through condenser 76. In a second mode,second condenser 78 exchanges heat from the thermal storage reservoir 70(or from fluid diverted from manifolds 75) through another side or coilof second condenser 78 to external ambient. In the second side or coilit may not be functioning as a condenser, in the sense that thetransport fluid may be single phase liquid, such as glycol or a glycolmixture, that is not intended to flash from liquid to vapour.

The heated material may be the transport medium to which heat isrejected from condenser 28. Whether as a decanting tap from thermalstorage reservoir 70, a pipe connection to hot manifold 71; or as asegregated flow path through a heat exchange coil heated by condenser 76or thermal storage reservoir 70, transport apparatus 60 may be operatedto carry defrost fluid that has been heated by the captured (i.e.,retained) waste heat output of machine 22, either directly or in atime-shifted, or time-delayed, manner from reservoir 70. The heattransfer transport medium used as the defrost fluid may be any suitablefluid. For this purpose, although other fluids might be used in eitherliquid or gas form, the transport fluid may be either polyethyleneglycol or a mixture that is partially glycol. In the refrigeration loopthe transport fluid may be a liquid, and may remain a liquid throughoutpassage through the defrost loop.

In the embodiment of FIG. 1, at least one of the refrigerating loadsfaced by heat exchanger 42, 44 or 46 is a moist air cooling load. Thenature of refrigeration is such that the possibility of frosting isexpected where the desired temperature of the materials to be cooled atthe output cooling load end is to be below the freezing temperature ofwater. To that end, any or all of heat exchangers 42, 44, 46 may be usedto chill air in a zone to be maintained below freezing; frost mayaccumulate on the air flow path side of the heat exchanger. From time totime, it may be necessary to remove the frost build-up in a defrostingcycle. In this discussion, “moist” means that the airflow has highenough absolute humidity for frost to form on a below-freezingtemperature surface.

In the embodiments shown and described, any or all of heat exchangers42, 44 and 46 may have three flow passages, or pathways, or coils, orcircuits, however they may be called. There is a first flow path 80, asecond flow path 82, and a third flow path 84.

First flow path 80 may be understood to be the flow path of the fluid ofthe cooling load, namely a moist air flow path. As may be understood,air may be urged along the flow path by a blower or fan 85 in a forcedair system.

Second flow path 82 may be understood to be the flow path of therefrigerant. This flow path may include a finned conduit 86 for thecooling medium. In one embodiment the coolant is a substance that is aliquid which may be converted to a gas at operating pressures, and thatis carried under pressure. Finned conduit 86 may be an evaporator forthat cooling medium. The cooling medium may be CO₂. Finned conduit 86(and the rest of the circuit of which it is part), may have the physicalproperty of being capable of containing fluids at high pressure. For thepurpose of this description, high pressure is a pressure in excess of250 psia. For CO₂ operation, although under various operating conditionsthe pressures may be higher or lower, the piping of the refrigerant flowpath may have the physical property of being operable not only in excessof 500 psia, but also in excess of 1000 psia, and possibly of operationat 2000 psia. In normal refrigerating operation, the refrigerant flowsthrough the finned tube, and the moist air to be cooled flows throughthe fin-work, with heat flowing from the load to be cooled and into thecoolant, reducing the enthalpy of the load and increasing the enthalpyof the coolant, possibly to such an extent as may cause the coolant toboil in whole or in part.

Third flow path 84 is a defrost flow path. It may include a finned coil88. Finned coil 88 may be parallel to finned coil 86, or it may sharethe same finwork as finned coil 86, or it may be immediately upstream offinned coil 86. Finned coil 86 may share the same fins or finwork asfinned coil 88. Finned coil 88 and the other components of the defrostcircuit, define a low pressure circuit or system, which has the physicalproperty of being operable up to 250 psia. It may be that the componentswill contain fluid at higher pressures, however the operating range maybe less than 100 psig, and may be less than 50 psia. It may be of theorder of less than 10 psig.

Third flow path 84 is segregated from second flow path 82. That is, theflow paths of the refrigerating and defrost circuits are segregated suchthat coolant from second flow path 82 is prevented from entering thirdflow path 84, and coolant from third flow path 84 is prevented fromentering second flow path, such that neither fluid can contaminate theother. Similarly, air from first flow path 80 cannot enter either secondflow path 82 or third flow path 84. In normal operation, second flowpath 82 operates at a lesser pressure than the third flow path 84. Innormal operation both second flow path 82 and third flow path 84 operateat pressures greater than first flow path 80.

To that end refrigeration apparatus 20 has a controller, which may be anelectronic controller, and which may be a programmed digital electroniccontroller. The controller is operable to direct chilled coolant throughsecond flow path 82 during normal refrigerating operation. Thecontroller is also operable to direct heated defrost fluid through thirdflow path 84. The controller is also operable to cease flow of chilledcoolant during a defrost cycle and to cease flow of defrost fluid duringa refrigeration cycle.

In a system with multiple cooling loads, such as 42, 44 and 46 (orhowever many more loads there may be) the controller is operableselectively to cycle the chilled coolant and defrost flows for each unitby causing valves to open an closed appropriately. That is, during adefrost cycle one cooling unit may be taken off-line at a time fordefrost, while the remainder continue to chill the cooling load. Whendefrost is complete on that unit, it may be brought back on-line, andthe next unit taken off-line and heated by defrost fluid, and so on inturn. Furthermore, where a rejected heat thermal energy storagereservoir 70 is employed, heat rejected during a chilling cycle may beretained and used to defrost the same heat exchanger previously chilled.It is not necessary that the compressors be run constantly. That is,there may be time periods where neither chilling nor defrosting isrequired, and the compressors may be off or dormant. Alternatively,there may be periods where chilling is required, but that cooling demandcan be met, if temporarily, by the quantity of chilled coolantpreviously accumulated in the receiver, whether in the cooling machineor in the coolant fluid distribution array, as may be. Similarly, thedefrost fluid pump 74 may be operated to circulate heated defrost fluidwhether the compressors are in operation or not. When operated in thismanner, the refrigeration system also permits heating load-shifting fromone time of day to another.

It may be that refrigeration apparatus 20 is part of a larger facilityor building 90. Referring to the general arrangement of FIG. 1, afacility such as a meat or fish packing plant 92 may include a zone tobe chilled by heat exchangers 42, 44, 46, etc., and may also includeother facilities such as a heated water tank, offices or meeting rooms,change rooms and showers, and so on. The refrigeration equipment may befully integrated with building mechanical systems in a combined heating,air conditioning and refrigeration system. It may be advantageous toemploy the rejected heat for additional purposes. It may be advantageousto employ the refrigeration apparatus as a heat pump to provide a sourceof heat for rejection, with an ice by-product that can be melted at asubsequent opportunity at which heat is required. That is, heating andcooling loads may not occur during the same time period, or may beunequally matched. Given that both heating and cooling loads may varyduring the day, it may be advantageous to provide a large amount ofrejected heat at one time of day, and a large amount of refrigeration atanother.

The building may include a meat or fish packing plant 92, a hot watertank 94, offices, conference rooms, or meeting rooms 96, change rooms98, showering facilities 100, or some combination thereof. The packingplant may include an ice builder 102, i.e., a facility designed to coolice into blocks or cubes, such as may be used, for example, in the foodservice industry or grocery stores, or within the plant itself. Such abuilding may have cooling loads (that is, a need for cooling orrefrigeration) and heating loads (that is, a need for heating) that mayvary with the time of day, the season of the year, the activitiesoccurring in the building, and the amount of sunshine per day. There maybe simultaneous heating and cooling loads, as when there is a coolingload to make ice, and a heating load to keep the occupied office ormeeting spaces warm. A space that requires heating at one time of daymay require cooling at another time of day.

In general, there will be time varying-cooling and heating load profilesfor building 90. The cooling load may tend to be lowest at night, andhigher during the day, particularly when the Sun is shining. During thenight the facility may be on “night set-back”, since the packingfacilities may be closed for the night, and need only be maintained inits condition. The heat loads may be less at night as well, given thegenerally cooler external ambient at night, the absence of a lightingload (assuming the lights are turned off at night).

Building 90 may be equipped with an energy management system, indicatedgenerally as 110, for responding to these environmental loadingconditions. Energy management system 110 may include refrigerationapparatus 20, as described above; a cold sink thermal storage member, orapparatus, indicated as “ice builder” 102; a hot water supply 104, suchas may be used to provide domestic hot water within the plant forwhatever uses; a building fan coil heating or air conditioning system106, a building heat pump 108, and a supplemental heating device 112,such as may be a back-up oil or gas fired boiler.

Cooling machine 22 of refrigerating apparatus 20 may be contained in aseparate building, or segregated structure, from the building orstructure in which the coolant distribution apparatus of items 40 and 50are located. This construction permits all devices through which theprimary system working fluid passes (which may be referred to as therefrigeration plant) to be segregated from, and to be separatelyventilated from, the enclosed building structure of the facility inwhich persons may be at work. In this way, a leak of the working fluidmay tend not to migrate into occupied areas of the facility, and may bevented to external ambient.

The coolant delivery apparatus, or array, so defined by items 40 and 50may be quite large in physical extent. In such a system use of a twophased, or phase changing, transport system may permit a large enthalpychange per unit mass of the distribution fluid, and a correspondingreduction in both the mass flow rate of that fluid, and of the pumpingpower requirement. The inventor considers CO₂ to be a suitabledistribution array heat transfer transport fluid. At normal operatingtemperatures between, for example −40 C and +200 C, however, CO₂ may bemaintained under quite high pressures. Those pressures may be well inexcess of 250 psia (1.75 MPa), and may typically be higher than 500psia. A typical operating regime may be in the order or 900-1200 psia.High pressure piping may be used, that piping having the physicalproperty of being operable at those pressures, and possibly at muchhigher pressures in the range of 2000-3000 psia. The high pressurepiping may be steel piping, and may be stainless steel piping. Inoperation, at very cold (−40 F) refrigerating conditions the CO₂ may beat about 130 psia. In general operation, the CO₂ pressure may besubstantially higher. This may be contrasted with a low pressure liquidpiping system, such as may carry glycol, which may typically operate at10 psig. Thus it is expected that the waste-heat defrost line willoperate at less than 100 psig., whereas the high pressure evaporatorside will operate at substantially higher pressures than 100 psig,typically greater than 120 psia, and almost always at greater than 130psia. It follows that to require defrosting, there must be cooling below32 F or 0 C in the evaporator or high pressure path. Similarly, todefrost, the low pressure defrost fluid must be warmer than 32 F or C.

In keeping with this, heat transfer transport medium conduit assemblies,namely the heating and cooling circuits emanating from segregatedstructure, such as low pressure defrost circuit piping of apparatus 60that carry defrost fluid to and from heat exchangers 42, 44, 46, maytend to be relatively low pressure conduits operating at modest positivepressure over ambient, carrying a more-or-less non-corrosive liquid heattransfer medium in the nature of a liquid coolant of relatively lowtoxicity, and low volatility, and such as may tend not to pose an undueenvironmental hazard if a leak should occur, such an antifreeze orantifreeze mixture, of which one type may be glycol or may includeglycol as a component of a mixture. Further, when used in the context ofthis application the term “glycol” may refer to a mixture of glycol andwater such as may be suitable for the operating range of the equipment,be it −30 C to +60 C, −40 C to +70 C or some other range. The pressureof the defrost piping may be less than 200 psia, less than 100 psig, maybe less than 50 psig (or 50 psia, as may be), and may typically be ofthe order of 10 psig. In the inventor's view it is desirable to keep thehigh pressure coolant circuit segregated from the low pressuredefrosting circuit such that, for example, defrost fluid does notcontaminate the coolant system.

Optional ice builder 102 defines a cold sink thermal storage member, orthermal capacitance member may, for brevity and simplicity be referredto as an “ice reservoir”. It may be that the ice reservoir is anaccumulation of ice, typically enclosed in an insulated wall structure,or tank. It may also be that it is not “ice” at all, but rather a brine,or an eutectic fluid, or some other medium such as may tend to have asignificant thermal mass, such that the ice reservoir may tend to workas a thermal capacitance that can be “charged up” by being cooled over aperiod of time, so that it may then have a large capacity to cool otherobjects at a later time. It may be that the ice reservoir employs aphase change material, such as a eutectic fluid as noted above, wherethere is a significant enthalpy drop between the warm state, possibly aliquid state, and the cool, or cold state, possibly a solid orquasi-solid state. A liquid freezing point would, for example, tend tobe just such a large enthalpy, narrow temperature range phenomenon.Where an eutectic material is used, it may be an eutectic having a phasechange temperature lying in the range of −40 to +20 F, or possibly inthe narrower range of −20 F to +0 F. The phase change medium may bewater, or an aqueous solution.

The arrangement described may tend to permit coolant to flow selectivelyto either ice builder 102 or to the elements of cooling loads 40, suchas evaporators 42, 44, 46, or to both in parallel depending on valvepositions in the system. Ice builder 102 may be a large insulatedenclosure, or box, or fluid-tight chamber through which liquid coolantcan be pumped. The enclosure may contain a large number of thermalstorage elements such as steel coils. They may be stacked to permitinterstitial flow of the liquid coolant, and segregate the heat transferstorage medium phase change material from the heat transfer transportmedium. Ice builder 102 has an inlet, and an outlet, such that coolantfed in at the inlet may tend to work its way through any of a largenumber of possible flow paths by wending about the collection, orstacked array, to the outlet, this process being accompanied by heattransfer between the diffusely moving liquid and the thermal storagemedium.

Thermal storage reservoir 70 is a large heat exchange fluid heattransfer medium stratification reservoir, or tank. The cold side loopdrawing hot coolant from the outlet of condenser 76 is carried to thehot side inlet near the top of reservoir 70, and may be drawn out at therelatively lower temperature the outlet located near the bottom ofreservoir 70, through such pumps as may be used, and back to the inletof evaporator 34.

Thermal storage reservoir 70 is a reservoir in which the rejected-heatside heat transfer fluid transport medium may settle and stratifyaccording to temperature. Thus hot return flow from condenser 76 isadded to the top of thermal storage reservoir 70, and cooled coolantdirected to the inlet of condenser 76 is drawn from the bottom ofthermal storage reservoir 70. Similarly, hot fluid for direction to thevarious heating loads is drawn from the upper region of storagereservoir 70, and returned to the bottom.

On occasions where there may not be sufficient rejected heat availablefrom condenser 76 to meet all of the heating loads of the facility 20,or where the temperature of the heat rejected is not fully sufficient tomeet the temperature requirements of, for example, a radiant or fan coilheater or a hot water heater, that unmet demand may be met by theemployment of a supplemental heating device 112, such as may be an oilor gas fired boiler. In this embodiment supplemental heat, for defrostor such other purpose as may be, in whole or in part, may be employed inthe event that refrigeration apparatus 20 is not in service, and analternate heat source is required. To that end, pumps may urge coolantfrom thermal storage reservoir outlet manifold 73 to the boiler. In theevent that extra heating is not required, the coolant may pass throughthe supplemental heating device, or through a bypass, without theheating element being in operation. After leaving the supplementalheating device, the fluid medium, having had a temperature boost (ornot, as may be appropriate in the circumstances), may be directed to apump such as may be used to urge the warmed coolant through the buildingfan coil forced air heating system, such as may be used in the facility,offices, and so on. At some times of year this system may be used toprovide heating, and at other times of year to provide cooling (e.g. toact as an air conditioner), such as when coolant from ice builder 102 isdirected through cooling circuit of apparatus 50 and the building fancoil and returned. When used for heating, coolant in apparatus 70exiting the fan coil heating system is carried along return line to theinlet manifold.

Alternatively, or additionally, warm coolant leaving the supplementalheating device may be directed through building radiant zone heatingapparatus such as may be installed in the various rooms of the facility.

Operation of apparatus 20 is governed by an electronic control system,such as may be termed energy management system 110, that includes acontroller, and an array of sensors such as may include (a) temperaturesensors; (b) pressure sensors; (c) humidity sensors; (d) volumetric flowrate sensors; (e) thermostat settings; (f) external ambient conditionsensors (g) solar sensors; and (h) a clock, or clocks. The use oftemperature and pressure sensors in refrigeration apparatus permits theoperating statepoints to be known, and adjusted, according to existingheating and cooling demands, and according to anticipated demand such asmay be determined from historic demand parameters stored in memory, andon the basis of external weather conditions.

The electronic control system may include a memory having climatic datafor the site of installation, including sun rise and sunset times forthe location, and it may have stored ambient temperature and pressureinformation from recent days for use in extrapolating thermal loadmanagement estimates. It may include setting temperatures for thevarious heat sinks and heat sources. The memory data may include datafor working fluid pressure, temperature, enthalpy, entropy, and density,from which other, intermediate statepoint conditions may beinterpolated. The electronic control system may also include programmedsteps for calculating the statepoints at which refrigeration apparatus20 might best operate for given loading conditions, or expected loadingconditions based on time of day, weather, and historic demand.

The electronic controller may assess heating and cooling loadsthroughout the facility. Having done so, it may determine the outputheat rejection temperature at the thermal storage reservoir, and maysignal the various heat load pumps to operate as may be required. Wherethere is surplus heat rejection, the controller may cause the closedcircuit cooler to operate to soak up the extra rejected heat. Wherethere is insufficient rejected heat to meet the heating load demand, thecontroller may cause the supplemental heating element to operate toboost the temperatures in the heating system or systems. Where a largeramount of rejected heat is desired, and before causing the supplementalheating element to operate, the controller may poll the condition of icebuilder, may check against values stored in memory for expected heatingdemand, and may, if the ice builder is not fully charged (that is, it isnot at or below its low set point temperature, and not at the minimumtemperature that can be achieve by refrigeration apparatus 20). Providedthat the time of day, and the point in the expected load cycle isappropriate, the controller may then signal refrigeration apparatus 20to maintain a higher than otherwise high side pressure, withcorresponding higher rejection temperature, or it may cause thecompressor to run at a higher mass flow rate, while also causing theheating load pumps to operate at a higher flow rate, the net resultbeing a greater rate of heat transfer. Adjustment of the expansiondevice nozzle may also permit a change in upstream pressure to beobtained. That is, where a specific thermal rejection temperature isdesired to achieve, for example, an 80-95 F temperature in the radiantspace heating apparatus, the system may operate both to increasemassflow rate of the working fluid in the cooling machine 22, but, inaddition, to choke the system to yield a higher pressure in condenser 76to give a combination of higher temperature and higher mass flow rate.This may then be accompanied by direction of coolant from the hot sideof evaporator 34 to ice builder 102. In the event that greater heatingis required, the electronic controller may signal for supplemental heat.

Where ice builder 102 is used to provide cooling to the condenser side,the freezing point of the thermal storage medium may in somecircumstances be in excess of 32 F., but less than the desired heatrejection temperature of the condenser.

In an alternate embodiment, as shown in FIG. 2, an alternaterefrigeration apparatus is shown as 120. Apparatus 120 is substantiallythe same as apparatus 20, but differs therefrom in being a cascadesystem, rather than the volatile brine system of apparatus 20. That is,apparatus 120 has a first cooling cycle circuit 116, which includescompressors 24, 26; condenser 28; pressure drop apparatus 30, andevaporator 34. Apparatus 120 also has a second cooling circuit 118 orsecond cooling machine 122, which includes compressors 124, 126;evaporator 34 serving as the condenser 128 of second cooling circuit118; a pressure drop apparatus, such as a nozzle or valve 130; and acooling load output 132, namely that of cooling or refrigeration load40, and its evaporators 42, 44, 46. Second cooling circuit 118 may alsoinclude a receiver 136 mounted downsteam of nozzle 130 and upstream ofload 40. Second cooling circuit 118 may include a refrigerant pump 148operable to draw refrigerant from receiver 136 and to urge thatrefrigerant to load 40 (or to ice builder 102, if used). The return fromload 40 is directed back into receiver 136. Compressors 124, 126 drawfrom the vapour of receiver 136, and output compressed gas to condenser128, and so on. Thus second cooling circuit 118 is cascaded from firstcooling circuit 116 the through the shared heat exchange medium ofevaporator 34—condenser 128, both of circuits 116 and 118 having theirown respective compressor stages. The upper cascade cycle is defined bya system such as ammonia vapour cycle cooling machine 22, and the lowercascade cycle is defined by a system such as a CO₂ cycle machine insecond cooling circuit 118.

In a summary of one embodiment, an industrial refrigeration systemincludes an ammonia vapour cycle machine as cooling machine 22. A pairof compressors 24, 26 feed a heat exchanger, such as condenser 28, withthe condensate being collected in a high pressure reservoir 36. Workingfluid leaves the high pressure reservoir through an expansion valve, ornozzle 30, whence it passes into another heat exchanger 34 in which theammonia evaporates. The evaporated ammonia then flows back to thecompressors, and so on.

The use of ammonia in a distribution system inside an enclosed buildingmay not be desired. In the system illustrated there is a cooling arraysymbolised by cooling loads 40, which may be the cooling distributionsystem of a meat packing plant. It may be a CO₂ based array, in whichCO₂ at perhaps about 1000 psia (+ or −100 psi) is condensed to liquid inthe heat exchanger 34 that is cooled by the ammonia system. Theliquefied CO₂ then flows through a check valve and into the distributionpiping to cooling heat exchanger array cooling load elements 42, 44, 46.Flashed CO₂ returns to the cascade heat exchanger, where it is onceagain cooler.

The system includes a heat rejection and recapture circuit, namelythermal storage reservoir 70. In the embodiment the heat recapturesystem is a glycol system. In this system heat rejected from the ammoniaprimary system is carried by the glycol from the condenser 28, 76 to areservoir identified as a thermal equalizer tank 72.

As may be appreciated, from time to time the distribution array frostsup. In this example, the evaporators each have a CO₂ circuit and aglycol circuit. When there is a need to defrost the system, the flow ofCO₂ to the array is interrupted, and flow of hot glycol from the thermalequalizer is directed to the evaporators of the distribution systeminstead. This heats the evaporators, causing them to defrost.

In this embodiment, (a) the system uses three working fluids (NH₃, CO₂,Glycol); (b) two of the three fluids are two phase-change fluids; (c)The heat for defrost is stored in a reservoir; the heat for defrost istransported by a third fluid, namely the glycol; (e) The heat exchangerson the refrigeration array side have segregated flow circuits for theCO₂ and the glycol. Alternatively an HFC fluid, such as Freon or anHCFC, could also be used as one of the three fluids.

What has been described above has been intended illustrative andnon-limiting and it will be understood by persons skilled in the artthat other variances and modifications may be made without departingfrom the scope of the disclosure as defined in the claims appendedhereto. Various embodiments of the invention have been described indetail. Since changes in and or additions to the above-described bestmode may be made without departing from the nature, spirit or scope ofthe invention, the invention is not to be limited to those details butonly by a purposive construction of the appended claims as required bylaw.

1. A refrigeration apparatus having a heat exchanger, said heatexchanger having a first flow path for a moist air cooling load to bechilled; a second flow path defining an evaporator for a refrigerantfluid; and a third flow path through which to conduct a defrost fluid;said second and third flow paths being segregated from each otherwhereby refrigerant fluid in said second flow path is isolated fromdefrost fluid in said third flow path.
 2. The refrigeration apparatus ofclaim 1 wherein said first flow path is an ambient air pressure flowpath, said second flow path is a high pressure flow path, and said thirdflow path is a low pressure flow path.
 3. The refrigeration apparatus ofclaim 2 wherein said refrigerant fluid includes a heat transfertransport medium carried in said second flow path at a pressure of atleast 100 psia.
 4. The refrigeration apparatus of claim 3 wherein saiddefrost fluid is carried in said third flow path at a pressure of lessthan 100 psig.
 5. The refrigeration apparatus of claim 1 wherein saidrefrigerant fluid includes CO₂.
 6. The refrigeration apparatus of claim1 wherein said defrost fluid includes a fluid other than CO₂.
 7. Therefrigeration apparatus of claim 6 wherein said defrost fluid is aliquid, the liquid being a brine that includes glycol.
 8. Therefrigeration apparatus of claim 1, further comprising a coolingmachine, said cooling machine having a work input, cooling output, and aheat rejection output, said cooling machine having a working fluid thatis other than CO₂.
 9. The refrigeration apparatus of claim 1 whereinsaid third flow path is operatively connected with a heat rejectionoutput of said refrigeration apparatus whereby, in operation, said heatrejection output is connected to heat the defrost fluid to be conductedthrough said third flow path.
 10. The refrigeration apparatus of claim1, further comprising a controller operable selectively to directrefrigerant fluid to said heat exchanger during a first time period, andto direct defrost fluid to said heat exchanger during a second timeperiod, said second time period being different from said first timeperiod.
 11. The refrigeration apparatus of claim 1 wherein: saidrefrigeration fluid is at least predominantly CO₂; said defrost fluid isa brine that is other than CO₂; and said third flow path includes aportion in which said defrost fluid is heated by recaptured waste heatrejected from said refrigeration apparatus.
 12. The refrigerationapparatus of claim 11 wherein said heat exchanger is a first heatexchanger, and said refrigeration apparatus further comprises: at leasta second heat exchanger; a cooling machine operable to chill CO₂ and toreject heat; said cooling machine having a working fluid, said workingfluid being at least predominantly ammonia; at least a first receiverreservoir in which one of (a) said working fluid, and (b) said CO₂ ismaintained in liquid phase; a thermal reservoir in which to storerecaptured waste heat rejected by said cooling machine; and controlapparatus operable selectively to direct chilled CO₂ to any of said heatexchangers, said control apparatus also being operable selectively todirect heated defrost fluid to respective ones of said heat exchangersat times other than when chilled CO₂ is being directed thereto.
 13. Therefrigeration apparatus of claim 1 further including a cooling machineoperable to chill CO₂ and to reject heat; and said cooling machine has aworking fluid, said working fluid being at least predominantly ammonia;whereby said CO₂ is chilled by heat exchange with cold ammonia, and saiddefrost fluid is warmed by heat rejected from hot ammonia.
 14. Therefrigeration apparatus of claim 1 further including a cooling machineoperable to chill CO₂ and to reject heat; and said cooling machine has aworking fluid, said working fluid being at least predominantly and HFC;whereby said CO₂ is chilled by heat exchange with cold ammonia, and saiddefrost fluid is warmed by heat rejected from the HFC.
 15. Arefrigeration apparatus comprising: a cooling machine having a workinput, a cooling output, and a heat rejection output; a first heatexchanger mounted to extract heat from a first cooling load, the firstcooling load having a frost point; a first transport apparatus connectedto carry a first heat transfer transport medium that has been chilled bysaid cooling output of said cooling machine to said first heat exchangerto cool said cooling load; a second transport apparatus connected tocarry a second, heated, heat transfer transport medium to said firstheat exchanger; said second transport apparatus being segregated fromsaid first heat transfer transport medium whereby said first and secondheat transfer transport media are segregated from each other; when saidfirst heat transport medium is directed to said heat exchanger, saidheat exchanger being operable at a temperature below the frost point ofthe first cooling load; and when said second heat transport medium isdirected to said heat exchanger, said heat exchanger being operable at atemperature above the frost point of the first cooling load.
 16. Therefrigeration apparatus of claim 15 wherein said second transportapparatus is connected to receive heat from said heat rejection output.17. The refrigeration apparatus of claim 16 wherein said apparatusfurther comprises a thermal storage member connected to receive heatfrom said heat rejection output, and said second transport apparatus isconnected to receive heat from said heat rejection apparatus that hasbeen stored in said thermal storage member.
 18. The refrigerationapparatus of claim 15 wherein said first transport apparatus is an highpressure fluid transport apparatus operable at pressure greater than 250psia., and said first heat exchanger defines an evaporator for the firstheat transfer transport medium.
 19. The refrigeration apparatus of claim15 wherein the first heat transfer transport medium is CO₂.
 20. Therefrigeration apparatus of claim 15 wherein the second heat transfertransport medium is other than CO₂.
 21. The refrigeration apparatus ofclaim 20 wherein the second heat transfer transport medium is a brinethat includes glycol.
 22. The refrigeration apparatus of claim 15wherein said cooling machine has a working fluid other than CO₂.
 23. Therefrigeration apparatus of claim 22 wherein said working fluid of saidcooling machine is at least predominantly ammonia.
 24. The refrigerationapparatus of claim 15 wherein said cooling machine is housed in a firstlocation, said first heat exchanger is housed in a second location, andsaid first location is independently ventilated to external ambient. 25.The refrigeration apparatus of claim 22 wherein said refrigerationapparatus includes a receiver reservoir for said working fluid of saidcooling machine.
 26. The refrigeration apparatus of claim 15 whereinsaid apparatus comprises a receiver reservoir for the second heattransfer transport medium.
 27. The refrigeration apparatus of claim 15wherein said first transport apparatus is a high pressure transportapparatus operable at pressures exceeding 250 psia.
 28. Therefrigeration apparatus of claim 15 wherein said second transportapparatus is a low pressure transport apparatus having an operatingenvelope pressure lower than 100 psig.
 29. The refrigeration apparatusof claim 15 wherein said apparatus includes at least a second heatexchanger mounted to extract heat from a second cooling load, the secondcooling load having a frost point.
 30. The refrigeration apparatus ofclaim 15 wherein said apparatus includes an ice-making refrigerationload.
 31. The refrigeration apparatus of claim 30 wherein saidice-making refrigeration load includes an ice-builder.
 32. Therefrigeration apparatus of claim 15 wherein said apparatus includes atleast an additional heating load and associated heat transfer transportapparatus connected to conduct rejected heat from said cooling machinethereto.
 33. The refrigeration apparatus of claim 32 wherein saidadditional heating load includes at least one of: (a) human activityspace heating; (b) a washing facility; (c) an ice melt pit; (d) aswimming pool; and (e) water heating.
 34. The refrigeration apparatus ofclaim 15 further comprising a controller operable selectively to directrefrigerant fluid to said first heat exchanger during a first timeperiod, and to direct defrost fluid to said first heat exchanger duringa second time period, said second time period being different from saidfirst time period.
 35. The refrigeration apparatus of claim 33 whereinsaid controller is operable selectively to direct chilled heat transfertransport medium fluid to any cooling load of said apparatus atdifferent time periods, and is operable selectively to direct warmedheat transfer transport medium fluid to any heating load of saidapparatus.
 36. The refrigeration apparatus of claim 15 wherein saidapparatus is operable to direct heat rejected by said cooling machine ata first time to said first heat exchanger at a later time,notwithstanding that at such later time said cooling machine may be oneof (a) shut down; and (b) dormant.
 37. A method of defrosting a heatexchanger, the heat exchanger having a first flow path for a moist aircooling load to be chilled; a second flow path defining an evaporatorfor a refrigerant fluid; and a third flow path through which to conducta defrost fluid; said second and third flow paths being segregated fromeach other whereby refrigerant fluid in said second flow path isisolated from defrost fluid in said third flow path, said methodcomprising conducting refrigerant fluid to second flow path in a firsttime period, during which frost accumulates on said heat exchanger; andconducting heated defrost fluid through said second flow path during asecond time period whereby the previously accumulated frost diminishes.38. The method of claim 37 wherein said method includes ceasing flow ofsaid refrigerant during flow of said defrost fluid.
 39. The method ofclaim 37 wherein the step of conducting the refrigerant fluid includesconducting the refrigerant fluid at a pressure of at least 120 psia. 40.The method of claim 37 wherein the method includes using CO₂ as therefrigerant fluid.
 41. The method of claim 37 wherein the step ofconducting heated defrost fluid occurs at a pressure less than 100 psig.42. The method of claim 37 wherein the method includes using a brine asthe defrost fluid, the brine including glycol.
 43. The method of claim37 wherein the method includes using a refrigerating apparatus to chillsaid refrigeration fluid, rejecting heat from said refrigerationapparatus while chilling said refrigeration fluid; and using saidrejected heat to heat the defrost fluid.
 44. The method claim 43 whereinsaid method includes saving heat rejected at a first time, and usingthat rejected heat to heat the defrost fluid at a later time.
 45. Themethod of claim 43 wherein said method includes employing ammonia as aworking fluid in the refrigeration apparatus.
 46. The method of claim 43wherein said method includes using heat rejected from said refrigerationapparatus also to address at least one additional heating load otherthan heating said defrost fluid.
 47. The method of claim 37 wherein saidmethod includes using refrigerant chilled by said refrigeratingapparatus to address at least one additional cooling load other thanchilling refrigerating fluid for chilling said moist air cooling load ofsaid heat exchanger.
 48. The method of claim 37 wherein there is aplurality of heat exchangers having moist air cooling loads, and saidmethod includes cycling refrigerant fluid and defrost fluid to saidplurality of heat exchangers selectively whereby each heat exchanger hasa defrost cycle.
 49. The method of claim 37 wherein the method includesusing a refrigeration apparatus to chill the refrigeration fluid, andthe method includes using CO₂ as the refrigeration fluid.